Inertially responsive switches



Nov. 16, 1965 c. YOUNG, JR 3,218,405

INERTIALLY RESPONS IVE SWITCHES Filed Jan. 31, 1964 lllllllllllllllll FIG. 1

Charles Youn Jz INVEN on ATTORNEYS United States Patent 0 3,218,405 INERTIALLY RESPONSIVE SWITCHES Charles Young, Jr., Silver Spring, Md., assignor to the United States of America as represented by the Secretary of the Navy Filed Jan. 31, 1964, Ser. No. 341,813 7 Claims. (Cl. 200-6153) (Granted under Title 35, U8. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to inertially responsive switches, and more particularly to escapement controlled, inertially responsive safety and arming switches for use in missiles.

inertially responsive switches have heretofore been proposed to perform safety and arming functions in missiles. In these prior art devices, an inertial mass is movably mounted for response to accelerations along the flight axis of the missile. The inertial mass is connected to switching contacts and operable to move these contacts to make and break various electrical circuits and arm the warhead of the missile upon acceleration thereof. In order to preclude inadvertent arming of the missile due to spurious accelerations, it has been proposed to retard the movement of the switching contacts by means of an escapement driven thereby to provide a suitable time delay. That is, the physical arrangement was such that while the inertial mass could rapidly respond to any acceleration applied to the missile, the movement of the switching contacts from a safe to an armed position was delayed by the action of the escapement. Thus, the prior art inertial switches not only had to see the design acceleration in the proper direction, but also had to see the design acceleration for a predetermined period of time in order for the switching contacts to be moved to the armed position and permit a locking device to lock up the inertial switch in the armed position.

While such prior art devices are operable, they have not proved to be satisfactory under all conditions of service. The basic problem causing failures of the prior art devices has been excessive wear of the escapement caused by failure or drying up of lubricants over long periods of storage and repeated exercise of the escapement due to spurious accelerations caused by normal handling since the inertial mass, and hence the switching contacts and escapement, will respond to every axial acceleration of the missile whether spurious or not. Various solutions such as improved lubricants and escapement materials have been proposed to eliminate this problem. These proposed solutions have merely served to reduce the magnitude of this problem rather than to solve it completely since missiles are generally stored for long periods of time and frequently handled prior to the actual firing thereof. Manifestly, it would be highly desirable if an inertially responsive switch could be provided which would embody the desirable features of the prior art devices while simultaneously eliminating the aforedescribed disadvantages.

It is therefore a primary object of the present invention to provide new and improved inertially responsive switches.

It is another object of this invention to provide inertially responsive switches wherein all moving parts with the exception of the inertial mass are locked in the safe position until the inertial mass sees its design acceleration.

It is a further object of this invention to provide escapement controlled inertially responsive switches in which the escapement is not exercised by spurious random accelerations.

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With these and other objects in view, the present invention contemplates a safety and arming switch having normally-open and normally-closed contacts operated by a follower coupled to an inertial mass by means of a tension spring and coupled to an escapement which provides a time delay in arming. To preclude unnecessary activation or exercise of the escapement due to movement of the inertial mass by vibration, one guide rod for the inertial mass and follower is rotatable about its axis and carries a pair of fixed pins projecting radially therefrom. One of these pins engages the follower and prevents movement of the follower due to vibration of the inertial mass which loads the tension spring. However, when the inertial mass sees its design acceleration, a cam carried by the inertial mass engages the second pin to rotate the guide rod and release the follower permitting the escapement to begin timing out. If the acceleration is maintained for a predetermined period of time, the follower releases a locking lever which holds the inertial mass in the armed position. Removal of acceleration prior to this time will permit compression springs bearing on the inertial mass to return the mass and follower to the safe position. In this event, a torsion spring on the guide rod rotates the guide rod back to its initial position to relock the follower.

Other objects, advantages and novel features of the invention will become readily apparent upon consideration of the following detailed description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a top plan view of an inertially responsive switch embodying the principle features of the invention and illustrating to advantage the locking and releasing pins which control movement of the follower;

FIG. 2 is a side elevation view of the switch of FIG. 1 and illustrates the inertial mass in the armed position and the follower intermediate its safe and armed positions; and

FIG. 3 is a sectional view taken along the line 33 of FIG. 2 and illustrates the locking lever for retaining the inertial mass and follower in the armed position when the escapement has timed-out.

Attention now is directed to the drawings, wherein like numerals of reference designate like parts throughout the several views, for a more detailed description of a preferred embodiment of the present invention. The inertial- 1y responsive safety and arming switch, designated generally by the reference numeral 10, comprises a base 11 having a pair of guide rods 12 and 14 mounted thereon; the guide rod 12 being rotatable about its longitudinal axis. An inertial mass 15 and a follower 16 are slidably mounted on the guide rods 12 and 14 for movement axially thereof (horizontally or laterally as viewed in the drawings). A tension spring 18 interconnects the inertial mass 15 and follower 16 and, upon movement of the inertial mass to the left as viewed in the drawings, tends to move the follower in the same direction. A pair of compression springs 19 and 20 are mounted on the guide rods 12 and 14, respectively, and normally urge the inertial mass 15 and follower 16 to their safe positions as illustrated in FIG. 1.

An electrically conductive strip 21 is mounted on the follower 16, and when the follower is in the safe position illustrated in FIG. 1, the conductive strip 21 closes a safing circuit between electrical conductors 22 and 24 and their associated terminals. A rack 25 (FIG. 3) is mounted on the follower 16 and is in mesh with a first gear 26 of an escapement 28 which is in turn secured in position on the base 11. The escapement 28 serves to provide a suitable time delay in the movement of the follower 16 to the left under the influence of the tension spring 18.

A locking pin 29 projects radially from the guide rod 12 and normally serves to engage a projecting portion 30 on the follower 16 to lock the follower in a safe position as long as the guide rod 12 remains in the position shown in FIG. 1 of the drawings. A torsion spring 31 connected between the base 11 and a spring pin 32 on the guide rod 12 normally urges the guide rod 12 to the position shown in FIG. 1. A releasing pin 34 projects radially from the left-hand end of the guide rod 12 and, when engaged by a conically shaped cam 35 carried by the inertial mass 15 as shown in FIG. 2, serves to rotate the guide rod 12 to the position shown in FIG. 2 where the locking pin 29 no longer engages the projecting portion 36.

Operation In order that a better understanding of the invention might be had, its mode of operation will now be described. The switch is mounted in the missile with the switch positioned so that the rear of the missile would be to the left as the switch is viewed in the drawings. When the missile is fired and begins to accelerate, the inertia of the mass will cause it to move relative to the base 11 and in opposition to the tension spring 18 and compression springs 19 and 20 to the position shown in FIG. 2. This movement of the mass 15 causes the cam to engage the releasing pin 34- and rotate the guide rod 12 so that the locking pin 29 clears the projection 30. The follower 16 is then free to begin moving to the left under the influence of the tension spring 18 which was loaded by the movement of the inertial mass 15. The follower 16 is precluded from immediately moving to the armed position by the action of the escapement 28 which imposes a time delay on this movement. After the follower 16 has moved a short distance, the safing circuit is interrupted by movement of the conductive strip 21 out of engagement with the terminals of the conductors 22 and 24.

A locking lever 36 (FIG. 3) is pivoted on a shaft 38 and is provided with a torsion spring 39 which normally urges rotation of the lever 36 about the shaft 38 in the direction shown by the curved arrow in FIG. 3. This movement of the locking lever 36 is normally precluded by a tang 40 formed on one end thereof projecting into a slot 41 formed in the under side of the follower 16. When the escapement has timed-out, however, but before the follower 16 is in the armed position, the tang 40 is then opposite an offset portion 42 of the groove 41. This permits the torsion spring 39 to rotate the locking lever 36 so that an end portion 44 thereof engages a locking surface 45 on the inertial mass 15 to lock the inertial mass 15 and hence the follower 16 in the armed position. When the follower is in this armed position, the conductive strip 21 closes an arming circuit by engaging the terminals of a pair of conductors 46 and 48 (FIG. 1). This completes the operation of the switch 10.

Thus it can be seen that the present invention provides a new and improved inertially responsive switch which is completely free of the inherent defects while retaining the advantages possessed by the aforedescribed prior art devices. Any acceleration less than the design acceleration (the minimum acceleration which will cause full movement of the inertial mass) acting on the inertial mass 15 would not cause movement of the follower 16 and exercise of the escapement 28 due to the locking action of the pin 29. Thus the ordinary accelerations on the mass 15 caused by transportation and handling of the missile will not cause movement of the follower and operation of the escapement since the compression springs 19 and 20 preclude engagement of the releasing pin 34 by the cam 35. Consequently, vibration of the inertial mass 15 under ordinary handling conditions does not impose wear on the escapement. Furthermore, even an acceleration of the inertial mass 15 equal to or in excess of the design acceleration caused by a sudden sharp jolt of the missile will not suflice to inadvertently arm the warhead of the missile. Accelerations caused by rough handling are inherently instantaneous in nature. Consequently, even though the cam 35 may momentarily engage the releasing pin 34 and unlock the follower 16, the immediate relaxation thereof will permit the compression springs 19 and 20 to force the inertial mass 15 back against the follower 16 and thus cause reversal of the escapement and reverse movement of the follower until the inertial mass and follower are again in the positions shown in FIG. 1. When the inertial mass and follower return to these positions, the torsion spring 31 rotates the guide rod 12 back to the position shown in FIG. 1 and the follower 16 is relocked by the locking pin 29.

It is to be understood that the above-described arrangements are simply illustrative of a preferred embodiment of the present invention. Numerous other arrangements may be readily devised by those skilled in the art to achieve a similar apparatus still embodying the principles of the present invention and falling within the spirit and scope thereof.

What is claimed is:

1. A safety and arming switch comprising a base,

an inertial mass slidably mounted on said base,

a follower slidably mounted on said base,

resilient means coupling said follower to said inertial mass for movement therewith,

contact means mounted on said follower and said base and operable to perform switching functions upon movement of said follower,

an escapement mounted on said base and connected to said follower for providing a time delay in the movement of said follower,

means normally locking said follower in the safe position to preclude exercise of said escapement by vibration of said inertial mass due to spurious accelerations, and

means on said base and operable upon maximum movement of said inertial mass for releasing said locking means.

2. A safety and arming switch comprising a base,

a pair of guide rods mounted on said base, one of said guide rods being rotatable about its longitudinal axis with respect to said base,

an inertial mass slidably mounted on said guide rods and movable from a safe to an armed position in response to a predetermined acceleration,

a follower slidably mounted on said guide rods,

a tension spring connecting said follower to said inertial mass for movement therewith,

contact means mounted on said follower and said base and operable to perform switching functions upon movement of said follower,

an escapement mounted on said base connected to and driven by said follower for providing a time delay in the movement of said follower,

a first pin projecting radially from said rotatable guide rod and normally locking said follower in the safe position to preclude exercise of said escapement by vibration of said inertial mass due to spurious accelerations,

a second pin projecting radially from said rotatable guide rod adjacent the armed position of said inertial mass, and

a cam carried by said inertial mass adapted to engage said second pin when the predetermined acceleration is applied to said mass and pivot said guide rod and said first pin to unlock said follower.

3. A safety and arming switch as defined in claim 2 wherein compression springs are provided on said guide rods for normally urging said inertial mass and said follower to the safe position.

4. A safety and arming switch as defined in claim 3 wherein a torsion spring is connected between said base and said rotatable guide rod for resetting said first pin in the locking position when said compression springs return said inertial mass and said follower to the safe position after a spurious acceleration.

5. A safety and arming switch as defined in claim 2 wherein a locking lever is pivoted on said base and is moved into engagement with said inertial mass by said follower after the escapement has timed-out to retain said inertial mass and said follower in the armed position.

6. A safety and arming switch comprising a base,

a rod rotatably mounted on said base,

a torsion spring normally biasing said rod to a safe position,

an inertial mass slidably mounted on said rod,

a follower slidably mounted on said rod,

a tension spring interconnecting said inertial mass and said follower,

a first pin projecting radially from said rod and engaging said follower to preclude movement thereof in response to varying tension in said tension spring caused by movement of said inertial mass due to vibration,

a second pin projecting radially from said rod and disposed on the other side of said inertial mass from said first pin,

a compression spring on said rod and interposed between said inertial rnass and said second pin to normally urge said inertial mass away from said second pin,

a cam secured to said inertial mass and adapted to engage said second pin and rotate said rod to an arming position where said first pin no longer restrains said follower from moving under the influence of said tension spring from a safe position to an armed position,

the spring rate of said compression spring being predetermined to preclude engagement of said cam and said second pin until said inertial mass is subjected to a predetermined acceleration,

contact means on said follower and said base for closing an arming circuit when said follower has moved to said armed position,

and an escapement mounted on said base and connected to said follower to provide a time delay in the movement of said follower.

7. A safety and arming switch as defined in claim 1 wherein said resilient means comprises a tension spring interconnecting the inertial mass and the follower.

References Cited by the Examiner UNITED STATES PATENTS 3,020,367 2/1962 Bariifi 2006l.53 3,117,196 1/1964 Vincent 200-6l.53 3,157,757 11/1964 Lorenz 2006l.53

BERNARD A. GILHEANY, Primary Examiner. 

1. A SAFETY AND ARMING SWITCHING COMPRISING A BASE, AN INERTIAL MASS SLIDABLY MOUNTED ON SAID BASE, A FOLLOWER SLIDABLY MOUNTED ON SAID BASE, RESILIENT MEANS COUPLING SAID FOLLOWER TO SAID INERTIAL MASS FOR MOVEMENT THEREWITH, CONTACT MEANS MOUNTED ON SAID FOLLOWER AND SAID BASE AND OPERABLE TO PERFORM SWITCHING FUNCTIONS UPON MOVEMENT OF SAID FOLLOWER, AN ESCAPEMENT MOUNTED ON SAID BASE AND CONNECTED TO SAID FOLLOWER FOR PROVIDING A TIME DELAY IN THE MOVEMENT OF SAID FOLLOWER, MEANS NORMALLY LOCKING SAID FOLLOWER IN THE SAFE POSITION TO PRECLUDE EXERCISE OF SAID ESCAPEMENT BY VIBRATION OF SAID INERTIAL MASS DUE TO SPURIOUS ACCELERATIONS, AND MEANS ON SAID BASE AND OPERABLE UPON MAXIMUM MOVEMENT OF SAID INERTIAL MASS FOR RELEASING SAID LOCKING MEANS. 